Flow rates are measured with a flat orifice plate which is installed in an orifice fitting. The orifice plate is held in position and sealed along its peripheral edge, to prevent fluids bypassing the orifice, by means of a seal ring. In order to ensure accuracy of flow rate measurement, the orifice must be concentrically disposed in the flow path. The American Gas Association (AGA) sets standards for orifice concentricity.
One of the focal points in improving concentricity, has been to develop improved seal rings for the orifice plates, that will maintain metal to metal contact. In the absence of metal on metal contact, elastomeric deformation under operating conditions will result in unacceptable movement. Examples of improved seal rings for orifice plates are illustrated and described in U.S. Pat. No. 5,085,250 (Kendrick 1992) and U.S. Pat. No. 5,186,474 (Jacobs 1993). The Kendrick reference teaches the use of grooves on an elastomeric seal ring and engagement ears on the carrier which moves the orifice plate in and out of the orifice fitting, to ensure metal on metal contact. The Jacobs reference teaches the use of circumferentially spaced metal locking pins to ensure metal on metal contact with the carrier.